U.S. patent application number 11/890377 was filed with the patent office on 2008-02-07 for backlight driving circuit with capacitive discharging current path and liquid crystal display with same.
This patent application is currently assigned to INNOLUX DISPLAY CORP.. Invention is credited to Jian-Hui Lu, He-Kang Zhou, Tong Zhou.
Application Number | 20080030147 11/890377 |
Document ID | / |
Family ID | 39028483 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080030147 |
Kind Code |
A1 |
Lu; Jian-Hui ; et
al. |
February 7, 2008 |
Backlight driving circuit with capacitive discharging current path
and liquid crystal display with same
Abstract
An exemplary backlight driving circuit (20) includes a first
pulse generator (230), a second pulse generator (240), a
transformer (250) having a primary winding (251), a first
transistor (210), a second transistor (220), and a first capacitor
(290). The first transistor is a P-MOSFET. The first transistor
includes a gate electrode (211) connected to the first pulse
generator, and a drain electrode (213) connected to a first
terminal (252) of the primary winding. The second transistor is an
N-MOSFET. The second transistor includes a gate electrode (221)
connected to the second pulse generator, a source electrode (222)
connected to ground, and a drain electrode (223) connected to the
first terminal of the primary winding. The first capacitor includes
one terminal connected to a second terminal of the primary
winding.
Inventors: |
Lu; Jian-Hui; (Shenzhen,
CN) ; Zhou; He-Kang; (Shenzhen, CN) ; Zhou;
Tong; (Shenzhen, CN) |
Correspondence
Address: |
WEI TE CHUNG;FOXCONN INTERNATIONAL, INC.
1650 MEMOREX DRIVE
SANTA CLARA
CA
95050
US
|
Assignee: |
INNOLUX DISPLAY CORP.
|
Family ID: |
39028483 |
Appl. No.: |
11/890377 |
Filed: |
August 6, 2007 |
Current U.S.
Class: |
315/282 |
Current CPC
Class: |
H05B 41/2828
20130101 |
Class at
Publication: |
315/282 |
International
Class: |
H05B 41/00 20060101
H05B041/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 4, 2006 |
TW |
95128628 |
Claims
1. A backlight driving circuit comprising: a first pulse generator;
a second pulse generator; a transformer comprising a primary
winding; a first transistor, the first transistor being a P-channel
metal-oxide-semiconductor field-effect transistor, and comprising a
gate electrode connected to the first pulse generator, and a drain
electrode connected to a first terminal of the primary winding of
the transformer; a second transistor, the second transistor being
an N-channel metal-oxide-semiconductor field-effect transistor, and
comprising a gate electrode connected to the second pulse
generator, a source electrode connected to ground, and a drain
electrode connected to the first terminal of the primary winding of
the transformer; and a first capacitor, the first capacitor
comprising one terminal connected to a second terminal of the
primary winding of the transformer.
2. The backlight driving circuit as claimed in claim 1, wherein an
amplitude of the first pulse generator is about 18V, a working
frequency of the first pulse generator is about 50 KHz, and a duty
ratio of the first pulse generator is about 0.65.
3. The backlight driving circuit as claimed in claim 1, wherein an
amplitude of the second pulse generator is about 5V, a working
frequency of the second pulse generator is about 50 KHz, and a duty
ratio of the second pulse generator is about 0.35.
4. The backlight driving circuit as claimed in claim 1, wherein the
transformer is an ELL19 transformer.
5. The backlight driving circuit as claimed in claim 1, wherein the
first and second transistors are AP4511GH transistors.
6. The backlight driving circuit as claimed in claim 1, further
comprising a power supply, wherein the power supply is connected to
a source electrode of the first transistor and another terminal of
the first capacitor.
7. The backlight driving circuit as claimed in claim 6, wherein the
power supply is an 18-volt power supply.
8. The backlight driving circuit as claimed in claim 6, further
comprising a second capacitor, wherein the second capacitor
comprises one terminal connected to ground, and another terminal
connected to the power supply.
9. The backlight driving circuit as claimed in claim 8, wherein the
second capacitor is an electrolytic capacitor.
10. The backlight driving circuit as claimed in claim 8, wherein a
capacitance of the second capacitor is about 220 .mu.F.
11. The backlight driving circuit as claimed in claim 8, further
comprising a third capacitor, wherein the third capacitor comprises
one terminal connected to ground, and another terminal connected to
the power supply.
12. The backlight driving circuit as claimed in claim 11, wherein
the third capacitor is a multilayer ceramic capacitor.
13. The backlight driving circuit as claimed in claim 1, wherein a
capacitance of the third capacitor is 0.01 .mu.F.
14. The backlight driving circuit as claimed in claim 1, wherein
the first transistor is a P-channel enhancement mode
metal-oxide-semiconductor field-effect transistor, or a P-channel
depletion mode metal-oxide-semiconductor field-effect
transistor.
15. The backlight driving circuit as claimed in claim 1, wherein
the second transistor is an N-channel enhancement mode
metal-oxide-semiconductor field-effect transistor, or N-channel
depletion mode metal-oxide-semiconductor field-effect
transistor.
16. A liquid crystal display comprising: a liquid crystal panel; a
backlight module adjacent to the liquid crystal panel; and a
backlight driving circuit configured for driving the backlight
module, the backlight driving circuit comprising: a first pulse
generator; a second pulse generator; a transformer comprising a
primary winding; a first transistor, the first transistor being a
P-channel metal-oxide-semiconductor field-effect transistor, and
comprising a gate electrode connected to the first pulse generator,
and a drain electrode connected to a first terminal of the primary
winding of the transformer; a second transistor, the second
transistor being an N-channel metal-oxide-semiconductor
field-effect transistor, and comprising a gate electrode connected
to the second pulse generator, a source electrode connected to
ground, and a drain electrode connected to the first terminal of
the primary winding of the transformer; and a first capacitor, the
first capacitor comprising one terminal connected to a second
terminal of the primary winding of the transformer.
17. The liquid crystal display as claimed in claim 16, further
comprising a power supply, wherein the power supply is connected to
a source electrode of the first transistor and another terminal of
the first capacitor.
18. A backlight driving circuit comprising: a first transistor, the
first transistor being a P-channel metal-oxide-semiconductor
field-effect transistor; a first pulse generator connected to the
first transistor; a transformer having a primary winding, the
primary winding comprising a first terminal connected to the first
transistor; and a second terminal; a second transistor connected to
the first terminal of the primary winding, the second transistor
being an N-channel metal-oxide-semiconductor field-effect
transistor; a second pulse generator connected to the second
transistor; and a first capacitor connected to the second terminal
of the primary winding; wherein the first capacitor, the primary
winding of the transformer, and the second transistor cooperatively
form a charging current path when pulse signals from the first and
second pulse generators are high level signals; and the first
capacitor, the primary winding of the transformer, and the first
transistor cooperatively form a discharging current path when the
pulse signals from the first and second pulse generators are low
level signals.
19. The backlight driving circuit as claimed in claim 18, wherein
the first transistor is a P-channel enhancement mode
metal-oxide-semiconductor field-effect transistor.
20. The backlight driving circuit as claimed in claim 18, wherein
the second transistor is an N-channel enhancement mode
metal-oxide-semiconductor field-effect transistor.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a backlight driving circuit
that includes a capacitive discharging current path, and a liquid
crystal display (LCD) including the backlight driving circuit.
BACKGROUND
[0002] LCDs are commonly used as displays for compact electronic
apparatuses, because they not only provide good quality images but
are also very thin. The liquid crystal in an LCD does not emit any
light itself. The liquid crystal has to be lit by a light source so
as to clearly and sharply display text and images. Thus, a
backlight module and a backlight driving circuit for driving the
backlight module are generally needed for an LCD.
[0003] Referring to FIG. 3, a typical backlight driving circuit 10
includes an 18-volt power supply 160, a first pulse generator 130,
a second pulse generator 140, a first capacitor 190, a second
capacitor 170, a third capacitor 180, a first transistor 110, a
second transistor 120, and a transformer 150 having a primary
winding 151.
[0004] The first transistor 110 is a P-channel enhancement mode
metal-oxide-semiconductor field-effect transistor (P-MOSFET), which
includes a gate electrode 111 connected to the first pulse
generator 130, a source electrode 112 connected to the power supply
160, and a drain electrode 113 connected to a first terminal 152 of
the primary winding 151 of the transformer 150.
[0005] The second transistor 120 is an N-channel enhancement mode
metal-oxide-semiconductor field-effect transistor (N-MOSFET), which
includes a gate electrode 121 connected to the second pulse
generator 140, a source electrode 122 connected to ground, and a
drain electrode 123 connected to the first terminal 152 of the
primary winding 151 of the transformer 150.
[0006] The first capacitor 190 includes a terminal (not labeled)
connected to ground, and another terminal (not labeled) connected
to a second terminal 153 of the primary winding 151 of the
transformer 150. The second capacitor 170 includes a terminal (not
labeled) connected to ground, and another terminal (not labeled)
connected to the power supply 160 for filtering low frequency
interferences from the power supply 160. The third capacitor 180
includes a terminal (not labeled) connected to ground, and another
terminal (not labeled) connected to the power supply 160 for
filtering high frequency interferences from the power supply
160.
[0007] In operation of the backlight driving circuit 10, when pulse
signals from the first and second pulse generators 130, 140 are
both low level signals, the first transistor 110 is switched on,
and the second transistor 120 is switched off. The power supply
160, the first transistor 110, the primary winding 151 of the
transformer 150, and the first capacitor 190 cooperatively form a
charging current path. The power supply 160 provides primary energy
stored in the transformer 150 to increase a primary current of the
transformer 150, and charges the first capacitor 190. When the
first capacitor 190 and the primary winding 151 of the transformer
150 proceed to resonate in series, the primary current of the
transformer 150 reaches a maximal value. That is, a primary energy
storage of the transformer 150 reaches a saturated state. Then the
transformer 150 proceeds to release the primary energy stored
therein, and begins to charge the first capacitor 190. Thus, the
primary current of the transformer 150 progressively decreases.
When the first capacitor 190 is charged to 18V (18 volts), the
primary energy stored in the transformer 150 is completely
released, and the primary current of the transformer 150 is equal
to 0.
[0008] When the pulse signals from the first and second pulse
generators 130, 140 are both high level signals, the first
transistor 110 is switched off, and the second transistor 120 is
switched on. The first capacitor 190, the primary winding 151 of
the transformer 150, and the second transistor 120 cooperatively
form a discharging current path. The first capacitor 190 begins to
discharge, the transformer 150 begins to store primary energy
therein, and the primary current of the transformer 150
progressively increases. When the first capacitor 190 and the
primary winding 151 of the transformer 150 proceed to resonate in
series, the primary current of the transformer 150 reaches the
maximal value. That is, the primary energy storage of the
transformer 150 reaches the saturated state. Then the transformer
150 begins to release the primary energy stored therein, and the
first capacitor 190 continues to discharge.
[0009] In the charging current path formed by the power supply 160,
the first transistor 110, the primary winding 151 of the
transformer 150, and the first capacitor 190, the first capacitor
190 is easily charged to 18V because the current passing
therethrough is a high current. Moreover, the first transistor 110
is a P-MOSFET having a large essential resistance, which is
typically at least 0.1.OMEGA. (ohms). Therefore the first
transistor 110 has high power consumption, and correspondingly
dissipates a large amount of the power consumed in the form of heat
energy. Thus the first transistor 110 has a high working
temperature, which is liable to affect its performance. This in
turn means the reliability of the backlight driving circuit 10 may
be impaired.
[0010] What is needed, therefore, is a backlight driving circuit
that can overcome the above-described deficiencies. What is also
need is an LCD including the backlight driving circuit.
SUMMARY
[0011] In an exemplary embodiment, a backlight driving circuit
includes a first pulse generator, a second pulse generator, a
transformer having a primary winding, a first transistor, a second
transistor, and a first capacitor. The first transistor is a
P-channel metal-oxide-semiconductor field-effect transistor. The
first transistor includes a gate electrode connected to the first
pulse generator, and a drain electrode connected to a first
terminal of the primary winding of the transformer. The second
transistor is an N-channel metal-oxide-semiconductor field-effect
transistor. The second transistor includes a gate electrode
connected to the second pulse generator, a source electrode
connected to ground, and a drain electrode connected to the first
terminal of the primary winding of the transformer. The first
capacitor includes one terminal connected to a second terminal of
the primary winding of the transformer.
[0012] Other novel features, advantages and aspects will become
more apparent from the following detailed description when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The components in the drawings are not necessarily drawn to
scale, the emphasis instead being placed upon clearly illustrating
the principles of at least one embodiment of the present invention.
In the drawings, like reference numerals designate corresponding
parts throughout various views, and all the views are
schematic.
[0014] FIG. 1 is a block diagram of an LCD according an exemplary
embodiment of the present invention, the LCD including a backlight
module, a backlight driving circuit for driving the backlight
module, and a liquid crystal panel.
[0015] FIG. 2 is a circuit diagram of the backlight driving circuit
of FIG. 1.
[0016] FIG. 3 is a circuit diagram of a conventional backlight
driving circuit.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0017] Reference will now be made to the drawings to describe
preferred and exemplary embodiments in detail.
[0018] Referring to FIG. 1, an LCD 2 according to an exemplary
embodiment of the present invention includes a liquid crystal panel
40, a backlight module 30 located adjacent to the liquid crystal
panel 40 for providing a planar light source for the liquid crystal
panel 40, and a backlight driving circuit 20 for driving the
backlight module 30.
[0019] Referring also to FIG. 2, the backlight driving circuit 20
includes a power supply 260, a first pulse generator 230, a second
pulse generator 240, a first capacitor 290, a second capacitor 270,
a third capacitor 280, a first transistor 210, a second transistor
220, and a transformer 250 having a primary winding 251.
[0020] The first transistor 210 is typically a P-channel
enhancement mode metal-oxide-semiconductor field-effect transistor,
which includes a gate electrode 211 connected to the first pulse
generator 230, a source electrode 212 connected to the power supply
260, and a drain electrode 213 connected to a first terminal 252 of
the primary winding 251 of the transformer 250.
[0021] The second transistor 220 is typically an N-channel
enhancement mode metal-oxide-semiconductor field-effect transistor,
which includes a gate electrode 221 connected to the second pulse
generator 240, a source electrode 222 connected to ground, and a
drain electrode 223 connected to the first terminal 252 of the
primary winding 251 of the transformer 250.
[0022] The first capacitor 290 includes a terminal (not labeled)
connected to the power supply 260, and another terminal (not
labeled) connected to a second terminal 253 of the primary winding
251 of the transformer 250.
[0023] The second capacitor 270 includes a terminal (not labeled)
connected to ground, and another terminal (not labeled) connected
to the power supply 260 for filtering low frequency interferences
from the power supply 260. In the exemplary embodiment, the second
capacitor 270 is an electrolytic capacitor, and a capacitance of
the electrolytic capacitor is 220 .mu.F (microfarads).
[0024] The third capacitor 280 includes a terminal (not labeled)
connected to ground, and another terminal (not labeled) connected
to the power supply 260 for filtering high frequency interferences
from the power supply 260. In the exemplary embodiment, the third
capacitor 280 is a multilayer ceramic capacitor (MLCC).
[0025] In the exemplary embodiment, the power supply 260 is an 18V
power supply. An amplitude of the first pulse generator 230 is 18V,
a working frequency of the first pulse generator 230 is 50 KHz, and
a duty ratio of the first pulse generator 230 is 0.65. An amplitude
of the second pulse generator 240 is 5V, a working frequency of the
second pulse generator 240 is 50 KHz, and a duty ratio of the
second pulse generator 240 is 0.35. The first and second
transistors 210, 220 are typically AP4511GH transistors. The
transformer 250 is typically an EEL19 transformer.
[0026] In operation of the backlight driving circuit 20, when pulse
signals from the first and second pulse generators 230, 240 are
both high level signals, the first transistor 210 is switched off,
and the second transistor 220 is switched on. The power supply 260,
the first capacitor 290, the primary winding 251 of the transformer
250, and the second transistor 220 cooperatively form a charging
current path. The power supply 260 provides primary energy storage
stored in the transformer 250 to increase a primary current of the
transformer 250, and charges the first capacitor 290. When the
first capacitor 290 and the primary winding 251 of the transformer
250 proceed to resonate in series, the primary current of the
transformer 250 reaches a maximal value. That is, a primary energy
storage of the transformer 250 reaches a saturated state. Then the
transformer 250 continues to release the primary energy stored
therein, the power supply 260 continues to charge the first
capacitor 290, and the primary current of the transformer 250
progressively decreases. When the first capacitor 290 is charged to
18V, the stored primary energy of the transformer 250 is completely
released, and the primary current of the transformer 250 is equal
to 0.
[0027] When the pulse signals from the first and second pulse
generators 230, 240 are both low level signals, the first
transistor 210 is switched on, and the second transistor 220 is
switched off. The first capacitor 290, the primary winding 251 of
the transformer 250, and the first transistor 210 cooperatively
form a discharging current path. The first capacitor 290 begins to
discharge, the transformer 250 begins to store primary energy
therein, and the primary current of the transformer 250
progressively increases. When the first capacitor 290 and the
primary winding 251 of the transformer 250 proceed to resonate in
series, the primary current of the transformer 250 reaches the
maximal value. That is, the primary energy storage of the
transformer 250 reaches the saturated state. Then the transformer
250 begins to release the primary energy stored therein, and the
first capacitor 290 continues to discharge.
[0028] In summary, the backlight driving circuit 20 includes the
discharging current path formed by the first capacitor 290, the
primary winding 251 of the transformer 250, and the first
transistor 210. Because the first capacitor 290 has a
characteristic whereby it generally cannot be discharged
completely, the current passing through the first transistor 210 is
relatively low. Therefore the first transistor 210 has low power
consumption, and correspondingly dissipates a low amount of the
power consumed in the form of heat energy. Thus the first
transistor 210 can reliably operate with a low working temperature.
Moreover, the backlight driving circuit 20 further includes the
charging current path formed by the power supply 260, the primary
winding 251 of the transformer 250, and the second transistor 220.
Because the first capacitor 290 has a characteristic whereby it
generally can be charged completely, the current passing through
the second transistor 220 is relatively high. However, the second
transistor 220 is an N-MOSFET having relatively low essential
resistance, which is typically about 0.01.OMEGA.. Therefore the
second transistor 220 has low power consumption, and
correspondingly dissipates a low amount of the power consumed in
the form of heat energy. Thus the second transistor 220 can
reliably operate with a low working temperature. These advantages
mean that the reliability of the backlight driving circuit 20 and
the LCD 2 are improved.
[0029] In an alternative embodiment, the first transistor 210 can
be a P-channel depletion mode metal-oxide-semiconductor
field-effect transistor. In another alternative embodiment, the
second transistor 220 can be an N-channel depletion mode
metal-oxide-semiconductor field-effect transistor.
[0030] It is believed that the present embodiments and their
advantages will be understood from the foregoing description, and
it will be apparent that various changes may be made thereto
without departing from the spirit or scope of the invention or
sacrificing all of its material advantages, the examples
hereinbefore described merely being preferred or exemplary
embodiments of the invention.
* * * * *